1. Field of the Invention
This invention relates generally to arrowheads having opening blades, and more particularly to blade-opening arrowheads that prevent the razor sharp cutting edges of pivotal blades from becoming dulled or nicked by contact with their corresponding arrowhead bodies when the blades are in a retracted or closed in-flight position.
2. Description of Prior Art
Arrows have long been used for war, hunting and competitive sports. A conventional arrow has a shaft, a nock at one end that receives the bow string, an arrowhead or point that attaches to the opposite end, and fletchings. The fletchings are glued to the shaft near the nock end, and help to stabilize the arrow in flight by causing it to rotate. Arrowheads generally have a pointed forward end, and an opposite threaded shaft end that attaches the arrowhead to the arrow shaft. Arrowheads are also attached to the forward end of arrow shafts by glueing and other methods.
Arrowheads come in a variety of different sizes and configurations depending on their intended use. For example, there are specifically designed arrowheads for competitive target shooting, shooting fish, hunting birds or small game animals, and for hunting big game animals.
Arrowheads used for hunting kill the game animal by cutting vital organs such as the lungs and vascular vessels such as arteries, which causes rapid hemorrhaging and/or suffocation. Quick and humane kills are dependent on accurate shot placement, and upon the amount or volume of the animal tissue that is cut. Hunting arrowheads that cut more tissue are more lethal, and therefore are better. The volume of tissue that is cut is determined by the cutting diameter of the arrowhead, the number of blades it contains, and by the distance the arrowhead penetrates into the animal. The cutting diameter of an arrowhead is determined by how far each cutting blade extends outward from the arrowhead body. The further the blades extend outward the larger the cutting diameter is, and therefore the more cutting potential the arrowhead has.
A common type of arrowhead used in hunting is the fixed-blade arrowhead, which has a pointed tip end used for penetrating, and fixed blades or non-pivotal blades that each have a razor sharp edge for cutting. Conventional fixed-blade arrowheads blades are held in a fixed position on the arrowhead, and most such blades are replaceable. The replaceable blades attach to the arrowhead body in longitudinal grooves called blade slots. The tip of the arrowhead may be separably attachable to the arrowhead body or may be integral with it. Arrowheads for hunting are generally known as broadheads.
Another popular type of arrowhead for hunting is the blade-opening arrowhead. Blade-opening arrowheads are generally known as mechanical broadheads. Blade-opening arrowheads, like conventional fixed-blade arrowheads generally have an elongated arrowhead body, a tip end, and a threaded opposite end. The blades of blade-opening arrowheads have an attachment end which attaches the blades to the arrowhead body by a pivot pin, so that the blades can pivot or rotate in a plane between a closed position and an open position. The blades of blade-opening arrowheads are also received in blade slots, which are machined or formed into the side of the arrowhead body. When the pivotal blades of blade-opening arrowheads are retracted or folded into the closed position, a substantial majority of each blade is generally housed within its corresponding blade slot. This feature gives blade-opening arrowheads the ability to attain significantly increased aerodynamic performance over fixed-blade arrowheads, due to the significantly decreased exposure the retracted blades have with the air when the arrow is rotating while in flight. Such increased aerodynamic performance results in the desirable features of: faster shooting arrows, flatter arrow trajectories, increased penetration energy and enhanced repeatability of accuracy, while also providing a wide diameter cut in the game animal when the razor sharp blades open at impact with the animal.
To hold the blades of blade-opening arrowheads in the retracted position during flight until the arrowhead penetrates the animal, annular retention members such as O-rings are most commonly used. Other commonly known annular retention members are, rubber bands, tight fitting plastic sleeves, tape, heat-shrinkable fitting plastic sleeves, and other wrap materials. Such conventional O-rings and the like are stretched around the outside of the blades when the blades are folded into the closed position, and exert an inward directed resistive force or a closing force against the blades which holds the blades in the retracted position. In addition to conventional O-rings and the like, there are several other blade retention systems know to the art, such as the use of magnetism, springs, leaf springs, friction detents and other frictional mechanisms.
Blade-opening arrowheads also come in a variety of different types and styles. The most common type of blade-opening arrowhead has blades that are pivotally connected to an arrowhead body at a location near the rear end of the arrowhead body. This makes it so that when the blades are folded into the retracted position a leading blade end positioned near the tip of the arrowhead protrudes outward from the arrowhead body. The leading blade ends of such blade-opening arrowheads rotate away from the arrowhead body in a rearward direction when penetrating an animal. Particularly, the leading blade ends catch on the animal's surface and serve to lever or rotate the blades into the open position, thus exposing the sharp cutting edges of the blades and cutting the animal. In such blade-opening arrowheads when the blades are folded into the retracted position each blade is rotated toward the arrowhead body in a forward direction and is received within its blade slot so that the section of the blade having the sharpened cutting edge thereon is seated next to the arrowhead body. With this type of blade-opening arrowhead when the blades are in the retracted or in-flight position the sharp blade edges abut against the arrowhead body or arrowhead tip.
It is desirable for the cutting edge of an arrowhead blade to be as sharp as possible so as to maximize the cutting ability of the arrowhead, and to therefore inflict the quickest killing wound to a game animal. It is also desirable for the cutting edge of an arrowhead blade to be as sharp as possible so as to maximize arrow penetration through the animal so that an easily distinguishable blood trail is created and recovery of the game animal is enhanced.
Arrowhead blade steel is hardened in a heat treating process before the fine razor cutting edge is ground on the blade edge. The more the steel is hardened the sharper a cutting edge the blade will be able to hold or have, but also the brittler the blade becomes. Arrowhead blade steel is generally hardened so as to maximize the sharpness of the blade edge but to yet keep the main section of the blade from becoming so brittle that it breaks or shears at target impact. A truly razor sharp virgin cutting edge has a very narrow angle between opposing blade edge sides or grind bevels, which are produced from the sharpening processes of grinding and/or honing, and therefore the thickness of steel near the cutting edge is very thin. The hardness necessary for arrowhead blade steel to produce an optimally sharp cutting edge while preventing brittleness breaking of the main arrowhead blade section generally is such that the thin section of steel at the very cutting edge is brittle enough or delicate enough to be easily damaged. This is especially evident when the fine cutting edge contacts relatively hard substances such as aluminum, steel or composites.
A major problem associated with blade-opening arrowheads of the type whose blades are retracted next to the arrowhead body such that the sharp cutting blade edges abut against the arrowhead body or arrowhead tip, is that each delicate razor blade edge gets damaged where it contacts the arrowhead body or arrowhead tip. This damage generally nicks the cutting edge or flattens the pointed angle of the discrete cutting edge to a dull blunt, which inhibits the arrowheads ability to cut and therefore decreases its lethality. To compound this problem the inward directed closing force exerted by conventional O-rings and the like against the outside edges of the blades when the blades are in the closed or in-flight position, forces the blades against the arrowhead body of conventional blade-opening arrowheads such that the delicate cutting edges are further pressed into the arrowhead body or tip and therefore are damaged or dulled even more so. Also, when an arrow is shot from a bow the pivotal blades experience a high impulse acceleration when the arrow is first released from the bow, which generates a opening force that acts upon the blades. This phenomena can slightly open the blades just enough to break the contact of the cutting edges with the arrowhead body or arrowhead tip, such that as the arrow begins to decelerate in its downrange flight the blades are slapped back into their closed position by the deceleration causing a closing force upon the blades. This slapping effect magnifies the dulling damage delivered to cutting blade edges of conventional mechanical broadheads.
It is apparent that there is a need for a blade-opening arrowhead that maintains a pivotal blade in a closed in-flight position in such a manner so as to not damage or dull the razor sharp cutting edge of the blade from contact of the cutting edge with the arrowhead body or arrowhead tip.